Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session B07: Suspensions: General IV |
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Chair: Bryan Quaife, Florida State University Room: 211 |
Saturday, November 23, 2019 4:40PM - 4:53PM |
B07.00001: Kinematics, Shape Dynamics, and Rheology of Soft Particle Suspensions Phani Kanth Sanagavarapu, Ganesh Subramanian, Prabhu Nott Fluid-structure interactions are ubiquitous in nature, finding applications in biology and engineering. Unlike rigid particles suspended in a fluid, deformable particles exhibit interesting shape dynamics when subjected to external flow fields [1]. Equally, the presence of small deformable particles in fluids can also significantly influence the rheological properties of the suspension [2]. We extend the analysis of Roscoe [2] from steady state to dynamics, as an alternative to the ``stress polarization'' technique used by Ref. [1]. Here, we present the influence of the externally imposed shear and axisymmetric extensional flows, the initial shape, orientation, and the elastic modulus of the particles on the shape dynamics of neo-Hookean elastic particles, and the rheology of the suspension. We consider initial orientations wherein the principal axis of the particle lies both in and out of the plane of the shear. [1] Gao, T., Hu, H. H., {\&} Casta\~{n}eda, P. P. (2012). Shape Dynamics and Rheology of Soft Elastic Particles in a Shear Flow. Physical Review Letters, 108, 058302. [2] Roscoe, R. (1967) On the rheology of a suspension of viscoelastic spheres in a viscous liquid. Journal of Fluid Mechanics, vol. 28, p.273-293. [Preview Abstract] |
Saturday, November 23, 2019 4:53PM - 5:06PM |
B07.00002: Hydrodynamic approach to compute reorientation times of NATA protein in different solutions: comparison with Molecular Dynamics and experiment Yevgen Melikhov, Maria L. Ekiel-Jezewska, Gouri S. Jas, Krzysztof Kuczera Molecular Dynamics (MD) is usually applied to compute translational and rotational diffusion coefficients and the corresponding rotational correlation time for peptides, such as N-acetyl-tryptophan-amide (NATA). Besides viscosity effects, specific solute-solvent interactions are present and a continuous change of the shape of NATA molecule is observed. MD approach allows simplification of this process segregating the whole dynamics into very limited number of conformers with corresponding time population and therefore, allowing extraction of Brownian dynamics for a particular conformer from MD. Now, knowing the structure of a particular conformer, we propose to study self-diffusion using hydrodynamic bead model, where each atom is represented by a separate bead. Such analysis adds to a better understanding of a fluid-molecule interaction. In this paper, we present comparison of experimental and computational (MD and hydrodynamic bead model) studies of reorientational motions of NATA in water, urea, GdmCl and proline. We found that rotational correlation times of NATA molecule in these solutions are very similar in MD and hydrodynamic bead model, matching experiment, if interactions between a co-solvent and NATA and ther effect on the local solute dynamic are taken into account. [Preview Abstract] |
Saturday, November 23, 2019 5:06PM - 5:19PM |
B07.00003: Shear induced gradient diffusivity of red blood cell suspensions Abhilash Reddy Malipeddi, Kausik Sarkar We compute the shear-induced gradient-diffusivity of red blood cells (RBC) from direct numerical simulation using a dynamic structure factor approach. Macro-scale phenomena, such as diffusivities, result from the micro-scale dynamics of RBCs. RBCs in shear flow exhibit extremely rich and complex motion such as tank-treading, tumbling and swinging. They affect the shear-induced diffusivity analyzed here. As the shear rate increases, the diffusivity increases initially due to the increased deformability of the cells, and thereby enhanced interactions between them. On further increase of the shear rate, a transition point is reached where the diffusivity briefly decreases before increasing again. The decrease corresponds to the transition of the single cell dynamics from the tumbling regime to the tank-treading regime. During tumbling of an RBC, due to the larger swept volume of the tumbling shape, its effective size and correspondingly the length scale for diffusion is larger than what is indicated by the cell volume. In the tank-treading regime, this effect is absent resulting in lowered diffusivity. [Preview Abstract] |
Saturday, November 23, 2019 5:19PM - 5:32PM |
B07.00004: The Effect of Rigid Cells on Blood Viscosity: Linking Rheology and Sickle Cell Anemia Zhe Feng, Antonio Perazzo, Yuan-Nan Young, David Wood, John Higgins, Zhangli Peng, Howard Stone Sickle cell anemia (SCA) is a disease that affects red blood cells (RBCs) within blood. Healthy RBCs are highly deformable objects that under flow can penetrate blood capillaries smaller than their typical size. In SCA there is an impaired deformability of some cells, which are much stiffer and with a different shape than healthy cells, and thereby affect regular blood flow. It is known that blood from patients with SCA has a higher viscosity than normal blood. However, it is unclear how the rigidity of cells is related to the viscosity of blood, in part because SCA patients are often treated with transfusions of variable amounts of normal RBCs and only a fraction of cells will be stiff. Hence, we report systematic viscosity measurements and numerical simulations of a suspension varying the fraction of RBCs affected by increased rigidity within a suspension of healthy cells. Our results show that there is a rheological signature within blood viscosity to clearly identify the fraction of rigidified cells within healthy deformable cells down to a 5{\%} volume fraction of rigidified cells. These results are relevant to better characterize SCA, provide useful insights relevant to blood transfusions, and, more generally, extend to the rheology of mixed suspensions having particles with different rigidities, as well as offering possibilities for developments in the field of soft material composites. [Preview Abstract] |
Saturday, November 23, 2019 5:32PM - 5:45PM |
B07.00005: Oriented suspension mechanics with applications to flow linear dichroism spectroscopy and pathogen detection Gemma Cupples, David Smith, Matthew Hicks, Rosemary Dyson Flow linear dichroism is a biophysical spectroscopic technique that exploits the shear-induced alignment of elongated particles in suspension. This talk is focussed around the broad aim of optimising the sensitivity of this technique by improving the alignment of these particles, with a specific application of a handheld synthetic biotechnology prototype for waterborne-pathogen detection. I will describe a model of steady and oscillating pressure-driven channel flow and orientation dynamics of a suspension of slender microscopic fibres. The model couples the Fokker-Planck equation for Brownian suspensions with the narrow channel flow equations, the latter modified to incorporate mechanical anisotropy induced by the particles. The linear dichroism signal is estimated through integrating the perpendicular components of the distribution function via an appropriate formula that takes the bi-axial nature of the orientation into account. For the specific application of pathogen detection via binding of M13 bacteriophage, I will explore the impact of the channel depth, width, pressure gradient and frequency of oscillations on the alignment in the system. I will also discuss the practical ability for oscillatory flow, compared to steady flow, for the analysis of smaller sample volumes. [Preview Abstract] |
Saturday, November 23, 2019 5:45PM - 5:58PM |
B07.00006: Semi-Permeable Vesicles with Adhesion Bryan Quaife, Ashley Gannon, Yuan-Nan Young We consider adhering, semi-permeable, two-dimensional elastic membranes that are permeable to water, but not to solutes. For inextensible membranes (vesicles), the adhesive force can result in the formation of doublets or clusters of vesicles, and this significantly alters the hydrodynamics and rheological properties of the flow. Moreover, depending on the flow condition and body forces, semi-permeability results in the vesicles either inflating towards a circular vesicle or deflating towards a long slender body. Suspensions of adhering semi-permeable vesicles under a variety of flow conditions will be presented and compared to suspensions of clean vesicles. [Preview Abstract] |
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